Abstract

With an aging population the frequency of postmenopausal fractures is increasing. Methods to enhance the repair of osteoporotic bone repair therefore become more important to reduce the society burden of care. We asked if absorbable collagen sponges containing recombinant human bone morphogenetic protein-2 (rhBMP-2) have the potential to enhance bone repair. We randomly assigned 40 rats into the ovariectomy and sham operation groups. A segmental defect was created in the right tibia 12 weeks after ovariectomy. rhBMP-2-containing absorbable collagen sponges were implanted into the defect in half of the animals in each group. We analyzed radiographs and histological sections and performed three-point bending tests to assess repair. Radiological scores in the rhBMP-2 applied rats were higher than those in controls at the end of 8 weeks after tibial osteotomy. The specimens failed under higher loads in the rhBMP-2-applied groups and histology revealed a higher fracture healing score, including callus formation, bone union, marrow changes, and cortex remodeling. We observed no adverse tissue responses such as fibrous connective tissue formation and inflammatory cellular infiltration. rhBMP-2 in absorbable collagen sponges enhanced bone repair in segmental tibial defects of ovariectomized rats. The sponges with rhBMP-2 appeared to enhance bone repair.

Radiological scores were higher in the OVX-BMP group compared to the OVX-CONTROL group at Week 8 of implantation. Radiological score of the SO-BMP group but not the SO-CONTROL group was higher than that of the OVX-BMP group.

(A) In the SO-CONTROL group about 50% of the fibrous tissue of the marrow was replaced by cartilage. Remodeling was mild to moderate and mild bridging was observed. Endochondral bone formation was observed (Stain, hematoxylin and eosin; original magnification ×100). (B) Callus formation across the defect and bone bridge union was almost full in the SO-BMP group. Adult type fatty marrow started to appear in this group (Stain, hematoxylin and eosin; original magnification ×100). (C) In the OVX-CONTROL group, callus formation was very mild. Bridging in the fracture line was sparse and fibrous tissue was dominating the marrow (Stain, Goldners’ Masson Trichrome; original magnification ×100). (D) In the OVX-BMP group well-organized young bone trabeculae were observed. Note that cortex remodeling was moderate to full and bone marrow was mostly replaced by new tissue. (Stain, hematoxylin and eosin; original magnification ×100). HE: Hematoxylin & Eosin; MT: Goldners’ Masson Trichrome; CB: Cortical Bone; SB: Spongy Bone; CT: Soft Callus/Connective Tissue; BM: Bone Marrow; Ca: Cartilage.